A、They often lead to war between religious groups. B、They keep certain occupations from thriving. C、They allow myths and half-tr

Why do we form opinions or attitudes about someone or something without really knowing much about them? Just hearing something good or bad about a person, a place or thing can influence our opinions, positively or negatively. But letting the opinions of another person determine what our opinions will be is dangerous. Forming opinions about someone or something before really knowing them well is called prejudice, "pre-" means before and "judice" refers to judgment. Hence, prejudice means to judge before having adequate knowledge. We can be prejudiced toward or against someone or something. In either case, we are only allowing ourselves to see half of the picture. Very few people or things in this world are all good or all bad. Prejudiced attitudes are usually based on myths, half-truths or incorrect information, and they are dangerous because they can keep us from learning the truth about someone or something. People form prejudices against others for many reasons, differences in their race, religion, gender or occupation.
    Prejudices keep people apart. They keep us from really knowing and understanding each other. We should feel proud of who we are and the group of people we represent. If feelings of pride begin to turn to feelings of superiority when we think that our group or our beliefs are better than those around us, however, then we begin to develop prejudiced attitudes that can be harmful. For example, the prejudiced attitudes of one group may keep another group from attending certain schools, from living in any neighborhood they want, or from getting a job or a promotion. Extreme feelings of prejudice have caused the deaths of innocent people. We are responsible for our own thoughts and opinions. When we let someone else tell us what to think about someone or something, we are giving up some control of our own lives. Before you form an attitude or opinion, find out for yourself about the person or the thing in question. Sometimes we don’t realize that we hold prejudiced attitudes toward or against someone or something. We need to carefully examine our lives and our fears, and ask ourselves whether our attitudes come from our personal knowledge and experience or from rumors and fear of the unknown. The good news about prejudice is that we are not born with it. Prejudiced attitudes and opinions develop over time, but with education and knowledge, we can replace our prejudices with cooperation and understanding.
    19.What does the speaker say about prejudice?
    20.Why does the speaker say prejudiced attitudes are dangerous?
    21.When does the speaker say we begin to develop prejudiced attitudes?